1. Field of the Invention
This invention relates to mechanisms for opening and closing the shutter of a magnetic disc cassette, and more particularly to such a mechanism which is adapted to be used with a magnetic disc cassette of the type in which the shutter is not given a bias force in a direction to close it.
2. Description of the Related Art
Of the magnetic disc cassettes there is one having a shutter arranged, when the cassette is not in use, to shield an opening portion through which a magnetic head enters the cassette.
The shutters of the magnetic disc cassettes of this kind are divided into two groups, one of which is given a bias force in a direction to close it by a spring or the like, and the other which is given no bias force.
The shutter of the type having no bias spring and the conventional opening and closing mechanism therefor are shown in FIGS. 1 to 3.
Referring to FIG. 1, a magnetic disc 1 is rotatably contained in a cassette 2 made of plastic or the like by molding techniques.
A center hub 3 is fixed to the central portion of the magnetic disc 1, and has its place in an opening portion 5 formed in the central portion of the cassette 2.
A PG pin 4 for indexing a phase of rotation of the disc 1 is buried in the center hub 3.
Opening portions 6 in which a magnetic head and others are to be fitted are formed in the upper and lower side panels of the magnetic disc cassette 2.
These opening portions 6 are opened or closed by a shutter 7 which is slidably fitted in such a way as to clamp the cassette vertically from the side edge thereof.
This shutter is slidable in directions indicated by arrows P and Q.
A rectangular opening portion 7a is formed in the side wall of the shutter 7.
A groove 8 is formed in the one of the sides of the cassette 2 on which the shutter 7 is provided.
Penetration holes 9 and 10 are formed in prescribed positions of the magnetic disc cassette 2 in order to determine the position when it is loaded in the apparatus.
In FIG. 1, an arrow C indicates the direction of loading of the cassette 2.
Mechanism for opening and closing the shutter is shown in FIGS. 2(a) to 2(e).
A member 73 for opening the shutter and a member 74 for closing the shutter are provided on the cassette holder (not shown). The opening member 73 is formed as, for example, a plate spring, and is fixed at its tail end side to the upper surface of the cassette holder. A pawl 73a whose cross-section is of the letter "L" shape is formed on the head end side, pointing downward.
An upward pointing bent portion 73c is formed in a side edge of the opening member 73. A projection 73e is provided on the upper surface of the opening member 73 at a point near the head end side.
The closing member 74 is superimposed on the upper surface of the head end portion of the opening member 73. Its one end is slidably, pivotally mounted on a pin 76 by means of an elongated slot 74b.
A pawl 74a extends downwardly of that portion of the closing member 74 which is adjacent to the elongated slot 74b and is then bent at right angles to the back surface of the opening member 73.
That side of the bent-off portion of the pawl 74a which is nearer to the entrance mouth for the cassette 2 is made as a slanted surface.
The opposite end of the closing member, 74 to that having the slot 74b is bent upward to define a portion 74c.
A spring 77 is tensioned between this bent portion 74c and the bent portion 73c of the opening member 73 to urge the closing member 74 to turn about the pin 76 in a counterclockwise direction as viewed in FIG. 2(a).
A cutout portion 74d is formed in that side edge of the closing member 74 which is nearer to the opening member projection 73e. The counterclockwise movement of the closing member 74 is limited when this cutout portion 74d engages the projection 73e.
That side edge of the cutout portion 74d which is nearer to the bent portion 74c is made as a slanted surface 74e.
The opening and closing mechanism of such construction as described above is mounted on the apparatus in such a condition that the pawls 73a and 74a confront the groove 8 formed in the side wall of the cassette 2.
Also, as shown in FIGS. 3(a) and 3(b), a pawl 72 is formed in the shutter 7 at a position ahead the opening portion 7a as viewed from the direction of loading, and extends toward the groove 8.
Further, the cassette 2 is provided with a lock lever 67 formed by synthetic resin or the like and its root end is fixed to a holding portion 68 formed in the cassette 2.
Also, the opposite end of the lock lever 67 is made the free end. A groove 67a is formed in its external surface. When the pawl 72 is fitted in the groove 67a, the shutter 7 is locked.
Before the cassette is loaded, the pawl 72 lies in the groove 67a of the lock lever 67, so that the shutter is in the locked state and the opening portion 6 is closed.
Next, the opening and closing operation of the shutter 7 will be explained.
At first, the cassette 2 starts to be inserted into the entrance of the apparatus, while the groove 8 is in alignment with the pawls 74a and 73a of the opening and closing mechanism, and, as it continues, the front end 70a of the shutter 7 is approaching the pawls 73a and 74a.
Then, the front end 70a of the shutter 7 contacts the slant surface of the pawl 74a. As it further advances, the closing member 74 is turned about the pin 76 in the direction indicated by arrow F in FIG. 2(a), or in the clockwise direction as viewed in FIG. 2(a), against the bias force of the spring 77.
And, the pawl 74a rides up on the side wall of the shutter 7.
During this operation, the pawl 74a does not contact with the lock lever 67, leaving the shutter 7 locked.
As the inserting of the cassette further advances, the pawl 74a presently enters the opening portion 7a by the force of the spring 77.
Meanwhile, at almost the same time, the pawl 73a of the opening member 73 pushes the lock lever 67 as shown in FIG. 3(c). Thereby the pawl 72 disengages from the groove 67a and the shutter 7 is released from the locking.
Also, at the same time when the locking is released, the pawl 73a contacts with the front end 70a of the shutter 7. After that, as the cassette is inserted, the shutter 7 moved to open position as shown in FIG. 3(d).
Usually, the ceiling portion of the cassette holder is provided with a presser spring for pushing the inserted cassette downward. Also, the height of the interior of the holder is larger than the thickness of the cassette.
The holder moves downward so that the position of the cassette is determined by location pins. In this case, the location pins also determines the height of the cassette.
After the cassette has stopped with its position and height being accurately determined by the location pins, the holder further moves slightly downward to permit the above-described presser spring to act on the cassette so that the accurate adjustment of the position of the cassette is insured.
This is generally called "overcharge". Since the opening and closing mechanism is rigidly mounted on the holder, this overcharging causes the mechanism to move downward along with the holder relative to the cassette which remains stationary. Therefore, the opening and closing pawls, the cassette and the shutter possibly can be damaged by this overcharge action.
For this reason, the opening member is made of a plate spring to allow for vertical deflection of the head end with its tail end fixed to the holder in order to avoid the possibility of such damage.
The closing operation of the shutter is performed in the following way.
When the cassette is pulled from the position of FIG. 3(d), because the pawl 74a lies in the opening portion 7a, and its side edge 7b is in abutting engagement against the side wall of the opening portion 7a, the shutter 7 is left stationary in the latched position, despite the cassette is moving outward. Thus, the shutter becomes closed as the cassette moves outward.
Then, the pawl 73a pushes the lock lever 67 as shown in FIG. 3(c). Then the pawl 72 enters the recess 67a, thereby the shutter is locked.
As the pulling out operation of the cassette further advances, for now, conversely, the closing member is pulled in the same direction as the pulling out direction of the cassette until the right hand end of the slot 74b strikes the pin 76.
During the leftward movement of the closing member 74, it is also turned in a direction indicated by arrow F in FIG. 2(a) by the slant surface 74e sliding on the projection 73e, and the pawl 74a withdraws from the opening portions 7a.
In such a manner, the shutter is opened and closed.
The above described structure uses an unnecessary number of parts, and is heavier than need be and militates against the desirable end of minimizing the size and weight of the opening and closing mechanism.
Also, the provision of a damage avoiding mechanism on the shutter opening and closing mechanism due to the overcharge of the cassette holder (not shown) when the cassette is loaded makes the structure more complicated, and of large size and heavy weight results.